Development of the scattering theory of X-ray absorption and core level photoemission

Abstract

Over the past two decades dramatic progress has been made in the development of the theory of X-ray and electron spectroscopies, e.g., X-ray absorption spectra (XAS), core-level X-ray photoemission spectroscopy (XPS), X-ray photoelectron diffraction (XPD), etc. A revolutionary advance was the development of efficient and accurate treatments of high-order, curved-wave electron multiple-scattering for high electron energies above a few hundred eV. These advances were applied first in the theory of X-ray absorption fine structure (XAFS) and subsequently in X-ray photoelectron diffraction (XPD). They also led to efficient ab initio codes which permit a quantitative interpretation of the spectra. Extensions have made it possible to treat magnetic effects, e.g., X-ray magnetic circular dichroism (XMCD) and its analog in XPD. Important progress has recently been made in understanding near-edge spectra, e.g. X-ray absorption near edge spectra (XANES), which often require a full-multiple-scattering treatment. Although such calculations had been highly demanding computationally, fast new approaches based on efficient Lanczos approaches and parallel processing have been developed to overcome this limitation.